This invention relates to an optical vibrometer and more particularly to an optical vibrometer in which the vibration of an object is measured by using a laser beam without contacting to the object.
FIG. 1 is a schematic view showing a conventional vibrometer using a laser beam. In FIG. 1, a laser beam generator 1 (laser beam source) generates a laser beam 4, which irradiates an object 3 to be measured, the vibration of which is . A measuring device 2 measures the laser frequency deviation. The irradiated laser beam 4 is reflected on the surface of the object 3. Then the reflected laser beam 5 returns to the measuring device 2. The returned laser beam 5 is detected by a vibration signal converter 6.
In the above-mentioned vibrometer, when the object 3 vibrates along the optical axis of the laser beam 4, the optical path length of the laser beam changes according to the axial vibration of the object 3. The optical vibration (optical frequency) changes depending on the changes in the optical path length. Therefore, the vibration of the object 3 along the optical axis of the laser beam 4 can be detected by measuring the variation of the optical frequency between the laser beams 4 and 5 using the measuring device 2 and the vibration signal converter 6.
In the above-mentioned vibrometer, however, the right angle vibration of the object 3 along the optical axis does not cause an optical frequency deviation. Therefore, the right angle vibration of the object 3 along the optical axis can not be measured by means of the vibrometer.
FIG. 2 is a schematic view showing an another conventional vibrometer using a laser beam. In FIG. 2, a laser beam generator 1 (laser beam source and the like) generates a laser beam 4, which irradiates a flat reflecting mirror 8 disposed on an object 3 to be measured. When the object 3 vibrates in a direction perpendicular to the reflective surface of the mirror 8, the point of reflection 9 of the reflected laser beam 5 changes. Therefore, by detecting the change of the point of reflection 9 of the reflected laser beam 5 of using an optical position measuring device 7, the vibratory condition of the object 3 can be measured.
In the above-mentioned vibrometer, however, if the direction of vibration of the object 3 is parallel to the reflective surface of the mirror 8, the reflection position 9 does not change. Accordingly, vibration parallel to the reflective surface of the mirror 8 can not be measured by means of such a vibrometer.
As mentioned above, in both of the conventional vibrometers, only uni-directional (one dimensional) vibration can be measured. Therefore, there arises a problem that if bi or tri directional (two or three dimensional) vibration is to be measured, it would be necessary to use two or three vibrometers.